The present invention is generally directed to conductive magnetic compositions and process thereof, and more specifically the present invention is directed to lightly colored conductive magnetic compositions, process thereof, and processes for the preparation of colored toner compositions, and inductive magnetic developers. In one embodiment, the present invention is related to magnetic particles with an average volume diameter of from about 0.1 micron to about 25 microns and more preferably from about 0.5 micron to about 6 microns, comprised of a core comprised of a magnetic particle, coated thereover with a lightly colored metal. In another embodiment, the present invention is related to magnetic particles with an average particle diameter size of from about 0.1 micron to about 25 microns and more preferably from about 0.5 micron to about 6 microns as measured by a Coulter Counter, which particles are comprised of a core comprised of a magnetic particle coated thereover with a lightly colored metal and overcoated thereover with a colorless metal halide, or oxide. Toner compositions comprised of resin particles, and the aforementioned magnetic particles are also encompassed by the present invention. In another embodiment, the present invention is related to a process for the preparation of magnetic particles comprised of a metal coated with another metal of a lightness value of from about 0 to about 60 units and preferably from about 0 to 30 units as measured by the Match-Scan II colorspectrometer available from Vidan Corporation. Moreover, in another embodiment, the colored metal coating is a light orange, brown, red, blue, or yellow color and displays a chroma of from about 0 to 40 units and a hue of from about 0 to 40 units as measured by the Match-Scan II colorspectrometer available from Vidan Corporation. In another embodiment, the present invention is related to a process for the preparation of lightly colored conductive magnetic particles of from about 0.1 micron to about 25 microns and more preferably from about 0.5 micron to about 6 microns, comprised of a core comprised of a metal; thereover a coating of a lightly colored metal formed by an in situ electrodeless electrochemical oxidation-reduction reaction between the magnetic particle surface and a solution of a soluble metal salt of the lightly colored metal ion. In yet another embodiment, the present invention is related to a process of preparing lightly colored conductive magnetic particles comprised of a core comprised of a metal; thereover a coating of a lightly colored metal formed by an in situ electrodeless electrochemical oxidation-reduction reaction between the magnetic particle surface and a solution of a soluble metal salt of the lightly colored metal ion; and thereover an overcoating of metal halide or metal oxide formed by an insitu oxidation reaction between the magnetic particle surface with a halide such as lodine or oxide such as peroxide. In another embodiment, the present invention is related to a process for the preparation of conductive magnetic particles wherein the overcoating of metal halide displays a lightness values of from about 0 to about 60 units and preferably from about 0 to 43 units; a chroma of from about 0 to 40 units and a hue of from about 0 to 40 units as measured by the Match-Scan II colorspectrometer available from Vidan Corporation. In another embodiment, the present invention relates to conductive lightly colored magnetic particles with conductivities of from about 0.1 (ohm-cm).sup.-1 to about 10.sup.-4 (ohm-cm).sup.-1. Another embodiment of the present invention relates to the use of the aforementioned lightly colored conductive magnetic particles in inductive magnetic developer compositions useful for ionographic processes. Also, in another embodiment the present invention relates to the use of these lightly colored conductive magnetic particles in magnetic colored toner compositions useful for xerographic processes.
The primary functions of the magnetic core particle is to provide appropriate magnetic properties such as from about 30 to about 120 emu per gram and more preferably from about 60 emu per gram to about 100 emu per gram. The primary function of the lightly colored metallic overcoating layer is to provide the desired conductivity of from about 10.sup.-4 (ohm-cm).sup.-1 to about 10.sup.-8 (ohm-cm).sup.-1, and in particular, to provide a light color to the magnetic particle with lightness values of from about 0 to about 60 units and preferably from about 0 to 40 units and more perferably from about 0 to about 6 units as measured by the Match-Scan II colorspectrometer available from Vidan Corporation. Effective metallic overcoating of the magnetic particle enables magnetic particles of very low tinctorial strength, such as a chroma of from about 0 to 40 units and a hue of from about 0 to 40 units as measured by the Match-Scan II colorspectrometer available from Vidan Corporation, enabling in embodiments the incorporation of these magnetic particles into colored toner compositions with complete, or substantially complete passivation of the coloring perturbation of the magnetic material on the colored toner composition. Coating of the core metal particle would lead to substantially the same, or higher conductivity for the coated magnetic particles enabling in one embodiment the incorporation of these magnetic particles into colored toner compositions where conductivity of from about 10.sup.-4 (ohm-cm).sup.-1 to about 10.sup.-8 (ohm-cm).sup.-1 is important for use in electrographic technologies. The primary function of the metallic halide or oxide overcoating layer is to provide the desired high conductivity of from about 0.1 (ohm-cm).sup.-1 to about 10.sup.-4 (ohm-cm).sup.-1, and in particular, to provide a light color with lightness of from about 0 to about 60 units, chroma of about 0 to about 40 units, and hue of about 0 to about 40 units, and preferably a colorless magnetic particle with lightness, chroma and hue of 10 units as measured by the Match-Scan II spectrometer. Effective metallic halide or oxide overcoating of the magnetic composite particle comprised of a metal coated with the aforementioned lightly colored metal enables magnetic particles of low tinctorial strength enabling in one embodiment the incorporation of these magnetic particles into highly conductive colored toner compositions with conductivity of from about 0.1 (ohm-cm).sup.- to about 10.sup.-4 (ohm-cm).sup.-1, and particularly useful in known inductive ionographic imaging systems, and technologies.
For a number of ionographic and electrophotographic imaging methods for printing and copying applications, it is desirable that the toner particles contain a magnetic material. Typical magnetic materials with appropriate magnetic properties for use in the preparation of such toner particles include metal powders of iron, cobalt, and nickel, metal oxide powders of iron or chromium, and ferrite particles of particle size in the range of about 20 nanometers to about 10 microns. Many of these particles, however, exhibit relatively poor electrical conductivity, such as from about 10.sup.-7 ohm-cm to about 10.sup.-14 ohm-cm, resulting in poor developability or no developability when employed in electrophotographic devices. Relatively higher electrical conductivity of from about 10.sup.-4 (ohm-cm).sup.-1 to about 10.sup.-8 (ohm-cm).sup.-1 is required for toner applications involving single component electrophotographic development systems. Additionally, yet even higher electrical conductivity is required for inductive signal component developers of from about 0.1 (ohm-cm).sup.-1 to about 10.sup.-4 (ohm-cm).sup.-1 for some ionographic development systems. The poor conductivity of these magnetic materials can be overcome by addition of highly conductive carbon black or tin oxide as external additives. However, the presence of external additives on magnetic pigments of high tinctorial strengths do not adversely affect the color quality of the magnetic pigment, other than black, and are of inferior color quality. Furthermore, the use of external conductive additives may display poor conductivity stability in both ionographic or electrographic processes. Furthermore, when carbon black is employed, it can restrict the use of such developer compositions to the production of black images only, and cannot be satisfactorily applied to the production of color images. In addition, many of the magnetic materials that have the required magnetic properties and the desired particle size for colored developer compositions are also black or darkly colored with relatively high tinctorial strength. Thus, these magnetic materials usually cannot be applied to the production of colored images, in particular lightly colored images, such as red, orange, yellow, green and magenta. Neutral color or matched color or lightly colored magnetic particles with suitable magnetic properties of from about 60 to about 100 emu per gram, and with resistivity of from about 0.1 (ohm-cm).sup.-1 to about 10.sup.-4 (ohm-cm).sup.-1 are not believed to be known. The conductive lightly colored magnetic particle compositions of the present invention, in one specific embodiment, can be generated by a direct preparative process involving an in situ electrochemical reaction between the surface of a core metallic magnetic particle, and a solution of a soluble salt of a lightly colored metal to produce an adherent coating metallic layer on the magnetic particle surface. In one embodiment, the coated magnetic particles are highly conductive, lightly colored with low tinctorial strength, and have suitable conductivity to meet all the requirements of magnetic toner compositions for color magnetic single component electrophotographic devices. Additionally, in another specific embodiment, the aforementioned conductive lightly colored magnetic particle comprised of a magnetic particle coated with a lightly colored conductive metal can be generated by a direct preparative process involving an oxidation reaction between the metal coating with a halide, such as iodine or oxide such as peroxide, or produce an outer coating of metal halide or metal oxide layer on the particle composite surface. In another embodiment, the aforementioned overcoated magnetic particles are highly conductive, lightly colored with low tinctorial strength, and have suitable conductivity to meet all the requirements of an inductive magnetic compositions for colored single component ionographic devices. For example, in a specific embodiment of this invention, the lightly colored magnetic particle is prepared by suspending about 1 mole percent by weight of iron metal powder of from about 1 to about 4 microns in an aqueous media containing copper(II)(valence of 2)sulfate of from about 0.2 mole percent by weight and catalytic amounts of sulfuric acid, effecting a metal coating of copper onto the core iron particle via an oxidation reduction reaction at a temperature of from about 10.degree. C. to about 30.degree. C. This aforementioned iron-copper magnetic particle is thus comprised of a core comprised of iron metal bound to a coating of copper metal resulting in a reddish color displaying a magnetic saturation of from about 80 emu per gram to about 85 emu per gram, and conductivity of from about 10.sup.-5 (ohm-cm).sup.-1. Subsequently, in another specific embodiment, the aforementioned iron-copper metal particle is treated with about 0.1 mole percent of iodine effecting an oxidation reaction between the outer metal copper coating and resulting in an outer coating of copper iodide at a temperature of from about 10.degree. C. to about 30.degree. C. This aforementioned magnetic particle is thus comprised of a core comprised of iron metal bound to a coating of copper metal and bounded thereover an overcoating of copper iodide layer resulting in a light reddish color displaying a magnetic saturation of from about 80 emu per gram to about 85 emu per gram, and conductivity from about 0.1 (ohm-cm).sup.-1 to about 10.sup.-4 (ohm-cm).sup.-1. Colored prints with chroma values of less than 40 units are considered poor quality to those in the art. In prior art magnetic toner compositions, the use of suitable magnetic materials displaying magnetic saturations of from about 60 to about 100 emu per gram, as well as displaying undesired high lightness values of from about 60 to about 100 units mask the effect of the pigment lightness, chroma and hue properties when incorporated with resin and pigments to obtain toner composition. The masking effect of the magnetic particles leads to poor quality colored prints with lightness, chroma and hue values of less than 40 units. In order to obtain good quality colored prints, it is desirable to use magnetic composites displaying suitable magnetic saturation of from about 60 to about 100 emu per gram as well as low lightness values of from about 0 to about 60 units, such that when incorporated into toner compositions with resins and pigments does not affect or perturb the high lightness, chroma and hue properties of the pigments, hence, generating good color quality prints with high lightness, chroma and hue values greater than 40 units.
The magnetic particles of this invention, and the toners thereof possess many advantages as illustrated herein. For example many prior art magnetic particles are coated externally to reduce their tinctorial strengths, but are only held statically to the surface and are not physically bound. Furthermore, such composites when utilized in the preparation of magnetic toners or developers do not retain their coated morphology and the external additives are removed partially or substantially from the metal particle during the process of the toner preparation yielding dull magnetic colored toner images. The magnetic particles, or compositions of the present invention in embodiments possess lightly colored metal or metal halide coatings bound to the surface and retain this morphology with low lightness of from about 0 to about 60 units and low tinctorial strengths of chroma values of from about 0 to 40 units and hue values of from about 0 to 40 units, and which during the preparation of colored magnetic toner compositions do not interfere or perturb the pigment's high lightness, chroma and hue, permitting rendering good excellent quality with substantially no background deposits, colored prints with high lightness, chroma and hue values of from about 60 to about 100 units as measured with the Match-Scan II spectrometer available fron Vidan Corporation.
The toner compositions of the present invention can be selected for a variety of known reprographic imaging processes including electrophotographic, especially xerographic, and ionographic processes. In one embodiment, the toner compositions can be selected for pressure fixing processes wherein the image is fixed with pressure. Pressure fixing is common in ionographic processes in which latent images are generated on a dielectric receiver such as silicon carbide, reference U.S. Pat. No. 4,885,220 (D/87316), entitled Amorphous Silicon Carbide Electroreceptors, the disclosure of which is totally incorporated herein by reference. The latent images can then be toned with the relatively conductive toner of the present invention by inductive single component development, and transferred and fixed simultaneously (transfix) in one single step onto paper with pressure. Specifically, the toner compositions of the present invention can be selected for the commercial Delphax printers, such as the Delphax S9000.TM., S6000.TM., S4500.TM., S3000.TM., and Xerox Corporation printers such as the 4060.TM. and 4075.TM. wherein, for example, transfixing is utilized. In another embodiment, the toner compositions of the present invention can be utilized in xerographic imaging apparatuses wherein image toning and transfer are accomplished electrostatically, and transferred images are fixed in a separate step by means of a pressure roll with or without the assistance of thermal or photochemical energy fusing.
In copending U.S. patent applications U.S. Pat. No. 5,135,832 (D/90192), U.S. Ser. No. 609,316 (D/90192Q) and U.S. Ser. No. 636,136 (now abandoned) (D/90152), the disclosures of which are totally incorporated herein by reference, there are illustrated colored magnetic toners comprised of magnetic particles of high tinctorial strength based on iron, chromium, or nickel dispersed in a core resin and containing whitening agents, such as titanium oxide, as well as a colored pigment, and which core is encapsulated by a polyurea shell containing conductive colorless additives on the surface.
In U.S. Pat. No. 4,443,527, the disclosure of which is incorporated herein by reference, there are disclosed magnetic particles such as chromium, nickel, iron, or cobalt oxides to produce yellow, brown or reddish color toner composition containing a mixture of finely divided reflecting pigment such as titanium dioxide coated on the metal particle as an external additive and contacting the masked particle with a suitable dye or pigment composition, wherein the dye or pigment coats or becomes embedded in said masking layer and dispersed in a fusible binder resin. Note that the masking coated layer and colored pigment is not bound to the seed magnetic particle and wherein the magnetic dye composite is conductive. In U.S. Pat. No. 4,623,602, substantially the same approach is disclosed except that the masking layer and colored layer contain a yellow fluoresecent dye, and binders are used in which the dye fluoresces. In U.S. Pat. No. 5,021,315, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for overcoating a finely dispersed metal oxide by an in situ process where the metal oxide is in the size range of 1 to about 50 microns. Magnetic oxide particles are coated by depositing a layer of finely divided submicron sized particles of copper oxide onto the surface of the core magnetic metal oxide particles, followed by a subsequent reduction of the deposited copper oxide on the surface of the magnetic particle to metallic copper, and wherein such composite displays a resistivity of from about 10.sup.5 to 10.sup.7 ohm-cm, or conductivity of from about 10.sup.-5 to 10.sup.-7 (ohm-cm).sup.-1. The processes of this patent enable, for example, red colored conductive magnetic particles suitable for colored toner compositions. However, only iron oxide is used as the seed magnetic particle and is of high tinctorial strength, and wherein the process involves the reduction of copper oxide to copper, and furthermore, conductivity of less than 10.sup.-5 (ohm-cm).sup.-1 cannot be obtained. The processes of the present invention in embodiments provides advantages over the prior art indicated in that, for example, there is provided a simple and direct electrochemical oxidation-reduction method to produce a metallic magnetic core particle coated with a conductive lightly colored metal layer, and that a subsequent in situ oxidation with a halide provides an overcoating of highly conductive particle of from about 0.1 to 10.sup.-4 (ohm-cm).sup.-1 and needed for use in specific inductive ionographic processes. Additionally, a lightness value of from about 0 to about 40 units needed in embodiments to obtain high color intensity prints can be achieved with the toners of the present invention.
The following United States patents are mentioned in a patentability search report for patent application U.S. Ser. No. 609,333 U.S. Pat. No. 5,135,832 (D/90192), the disclosure of which is totally incorporated herein by reference, relating to encapsulated toners, and entitled Colored Toner Compositions: 4,803,144, which discloses an encapsulated toner with a core containing as a magnetizable substance a magnetite, see Example 1, which is black in color, wherein on the outer surface of the shell there is provided a white electroconductive powder, preferably a metal oxide powder, such as zinc oxide, titanium oxide, tin oxide, silicon oxide, barium oxide and others, see column 3, line 59, to column 4; in column 8 it is indicated that the colorant can be carbon black, blue, yellow, and red; in column 14 it is indicated that the electroconductive toner was employed in a one component developing process with magnetic brush development, thus it is believed that the toner of this patent is substantially insulating; 4,937,167 which relates to controlling the electrical characteristics of encapsulated toners, see for example columns 7 and 8, wherein there is mentioned that the outer surface of the shell may contain optional surface additives 7, examples of which include fumed silicas, or fumed metal oxides onto the surfaces of which have been deposited charge additives, see column 17 for example; 4,734,350 which discloses an improved positively charged toner with modified charge additives comprised of flow aid compositions having chemically bonded thereto, or chemically adsorbed on the surface certain amino alcohol derivatives, see the Abstract for example; the disclosures of each of the aforementioned patents being totally incorporated herein by reference; and which according to the search report are not significant but may be of some background interest 2,986,521; 4,051,077; 4,108,653; 4,301,228; 4,301,228; 4,626,487; 3,590,000; 3,983,045; 4,035,310; 4,298,672; 4,338,390; 4,560,635; 4,952,477; 4,939,061; 4,937,157; 4,904,762 and 4,883,736, the disclosures of each of these patents being totally incorporated herein by reference.
There is a need for lightly colored conductive magnetic particles, and in particular lightly colored conductive magnetic particles for the preparation of colored magnetic toner compositions with many of the advantages illustrated herein. There is a need for conductive magnetic particles with high magnetic saturation strengths of from about 30 emu per gram to about 120 emu per gram and more preferably from about 60 emu per gram to about 100 emu per gram. Additionally, there is a need for conductive magnetic particles which display conductivity of from about 10.sup.-4 (ohm-cm).sup.-1 to about 10.sup.-8 (ohm-cm).sup.-1, particularly in xerographic process, and from about 0.1 (ohm-cm).sup.-1 to about 10.sup.-4 (ohm-cm).sup.-1, particularly in ionographic process. Furthermore, there is a need for lightly colored magnetic conductive particles with lightness value of from about 0 to about 60 units and preferably from about 0 to about 40 units measured by the Match-Scan II spectrometer available from Vidan Corporation. Moreover, there is a need for lightly colored magnetic particles which display low tinctorial strength of chroma such as from about 0 to about 40 units and hue from about 0 to about 40 units, and preferably may be colorless, such that the chroma, lightness and hue values are about 0 units. Moreover, there is a need for brightly colored magnetic toner compositions displaying bright red, orange, cyan, magenta and yellow color which contain resin pigments and the aforementioned lightly colored and low tinctorial strength conductive magnetic particles. Additionally, there is a need for lightly colored magnetic conductive particles with a diameter size of from about 0.5 micron to about 25 microns and more preferably from about 0.1 micron to about 6 microns as measured by the Coulter Counter. Another associated need resides in the provision of preparative processes for obtaining lightly colored conductive magnetic particles, which possess a particle size diameter of 0.5 micron to about 25 microns, a magnetic saturation strength of from about 30 emu per gram to about 120, and a conductivity of from about 10.sup.-4 (ohm-cm).sup.-1 to about 10.sup.-8 (ohm-cm).sup.-1.